Theoretically, vegetable consumption could improve iron
status. First, vegetables contain iron. Second, when the
provitamin A carotenoids in vegetables improve vitamin A status,
the result could be increased iron levels. Most studies on
vegetable consumption have focused on improvements in vitamin A
status, and only very few have addressed iron status. From a
review of the literature and a recent study in Indonesia, we
conclude that the data on the effectiveness of vegetables to
improve the levels of both nutrients are inconclusive. The
bioavailability of both iron and provitamin A carotenoids might
be lower than expected. It is necessary to conduct other
intervention studies using plant foods, animal foods, and
fortified foods. In the meantime, other strategies that have been
proved to reduce iron and vitamin A deficiencies should continue.

Background

Food-based approaches to combat deficiencies of micronutrients
such as iron and vitamin A deserve great attention, because they
are likely to be sustainable in the long term, and the intake of
other nutrients will increase simultaneously. Few studies,
however, have evaluated the effectiveness of vegetables and
fruits to combat iron and vitamin A deficiencies.

Most studies with vegetables have focused primarily on vitamin
A status. A well-controlled study showed an increase in serum
retinol levels after subjects ate red sweet potato and dark green
leafy vegetables [1]. The increase in serum ß-carotene after
subjects consumed carrots was only 14% to 20% of the increment
after an equal dose of purified ß-carotene [2, 3], although it
was expected to be about 33%. Other investigators failed to
report any improvement of serum ß-carotene levels after feeding
the subjects carrots [4].

According to our recent literature review, evidence that
eating fruits and vegetables may improve vitamin A status is
inconclusive [5]. Because vegetables contain iron, increased
consumption of vegetables would be expected to improve iron
status, although the increase might be small because the
bioavailability of iron in these foods is poor [6]. It is also
possible that if vitamin A status improves after eating
vegetables, iron status will do so as well, because improving the
vitamin A status of anaemic subjects also increases haemoglobin
levels [7, 8]. Ivygourd (1.1 mg ß-carotene/day) given for a
relatively short period of two weeks did not improve haematocrit
level [9], whereas supplements of vegetables and purified
ß-carotene (1.2 mg/day) given for three months [10], and papaya
(1.2 mg ß-carotene/day). amaranth (1.2 mg ß-carotene/day), or
retinol (300 g/ day) given for two months [11], improved
haemoglobin concentrations. Another study (Muhilal and Karyadi,
personal communication) found no improvement in concentrations of
serum retinol and haemoglobin after feeding vegetables (1.9 mg
ß-carotene/day) for 75 days, but salt fortified with retinol
(300 RE/day) improved serum concentrations of retinol and
haemoglobin.

Because the findings on the role of vegetables in improving
vitamin A status are inconclusive, and only very few studies have
investigated their effects on iron status, more research is
urgently needed to evaluate dietary approaches, especially those
using vegetables, for combating iron and vitamin A deficiencies.

Recent study in Indonesia

We recently investigated whether an additional daily portion
of local vegetables can improve iron and vitamin A status in
anaemic breastfeeding women in a rural area in the Bogor
district, west Java [12]. The intervention lasted 12 weeks. One
group received stir-fried vegetables, and a second group received
a wafer enriched with iron, ß-carotene, folic acid, and vitamin
C, to examine the effect of a similar amount of micronutrients in
a matrix with better bioavailability. A third group received a
non-enriched wafer to control for effects of additional energy
intake. Each of the 191 women had a breastfed child age 3 to 17
months, a baseline haematocrit below 38%, and a haemoglobin
concentration below 130 g/L as measured by the cyanmethaemoglobin
method.*

Assignment to the vegetable or wafer groups was done by
village, which was justified by the larger intra-village than
inter-village differences. The vegetable supplements contained
100 to 150 g of cassava leaves (Manihot utilissima), water
spinach (Ipomoea aquatica), spinach (Amaranthus viridis), or
carrots (Daucus carota). The wafers were wrapped in blue or red
foil and distributed double-blind. The compositions of the
prepared vegetable supplements and the enriched wafers as
analysed were as follows: all trans-ß-carotene: vegetables 3.5
mg, wafers 3.5 mg; iron: vegetables 5.2 mg, wafers 4.8 mg; folic
acid: vegetables 130µg, wafers 100µg; and vitamin C: vegetables
11 mg, wafers 22 mg. The control wafer contained less than 10% of
these micronutrients. The fat content of the vegetables was 7.8
g, that of the wafers 4.5 g.

Follow-up data were obtained for 175 women. None of them
suffered from clinical infections, but almost all had one or more
parasitic infestations. Compliance was ensured by observing the
women consume the supplement. Replacement of the participants'
own vegetable dishes was avoided by bringing the supplement in
the early morning, when the women would not usually eat
vegetables. That the vegetables really were a supplement was
ascertained by the following observations:

1. The intake of macronutrients, iron, and vitamin
A-rich foods, calculated from 24-hour recall
questionnaires, remained the same before and during the
intervention in all groups.

2. The weight loss was similar in the three groups.

3. The treatment effect was the same in subjects who
lost weight as in those who gained weight.

The iron status values, haematocrit, zinc protoporphyrin, and
serum concentrations of ferritin and transferritin receptor
measured at baseline, and the haemoglobin concentration at three
weeks, did not differ among the groups, except for a slightly
higher concentration of serum transferrin receptor in the
vegetable group compared with the control wafer group. Between
the third week and follow-up, the haemoglobin concentrations
increased in all groups (baseline mean 109 g/L; 95% confidence
interval (95% Cl) of the increment 7 to 10 g/L; n = 175). Between
baseline and follow-up, the serum transferrin receptor
concentration decreased in all groups (baseline median 4.25 mg/L;
95% CI of the decrement -0.6 to -0.3 mg/L; n = 174). The
haematocrit increased in the vegetable and enriched wafer groups.
The changes were not significant in all groups, but none of the
changes were different among the treatment groups (analysis of
covariance). All improvements in iron status seemed to be due to
regression to the mean, because all subjects were selected on the
basis of a low haemoglobin level, and to the recovery of blood
loss from pregnancy and delivery.

The baseline concentrations of retinol in serum and breastmilk
and of #-carotene in serum did not differ among the groups. The
retinol concentrations in serum and breastmilk of the enriched
wafer group showed large increments, one-third and twothirds,
respectively. These were significantly different from the changes
in the control wafer group and the vegetable group. Both
concentrations did not change in the vegetable group, and
breastmilk retinol showed a marginal increase in the control
wafer group. The serum ß-carotene concentration increased almost
fourfold in the enriched wafer group. It increased slightly but
without physiological relevance in the vegetable group, and it
remained unchanged in the control wafer group.

In summary, improvements in iron status were similar in the
three treatment groups, but a physiologically meaningful change
of vitamin A status occurred only in the enriched wafer group. It
seems that the contents of iron and vitamin C of the vegetables
(5.2 and 11.4 mg, respectively) and of the enriched wafer (4.8
and 21.5 mg, respectively) were too small to improve iron status.
The bioavailability of iron in vegetables is known to be poor
[6]. The enriched wafer contained carbonyl iron, the
bioavailability of which seems comparable with that of ferrous
sulphate [13] but might be reduced by incorporation in foods
[14].

The improvement of vitamin A status of the enriched wafer
group seems not to have improved iron status. However, for the
women with a baseline serum retinol level below 0.70 µmol/L, the
increase in haematocrit was significantly greater (p< .05) in
the enriched wafer group (95% Cl 0.01 to 0.02, n = 20), compared
with the control wafer group (95% CI -0.01 to 0.01, n = 24), or
the vegetable group (95% CI 0.00 to 0.01, n = 19). Increases in
haemoglobin levels showed a similar but not significant trend,
whereas other iron status values showed no differences among the
groups.

The difference in change of iron status between the group that
improved in vitamin A status and those that did not was smaller
than that observed in other studies. A possible explanation is
that higher doses of vitamin A were given in the other studies-a
single dose of 110,000 RE [7] or a daily dose of 2,400 RE for
eight weeks [8]-which might have caused a change in iron status
within a shorter period of time. The very small variation in
serum ß-carotenes response in the vegetable group suggests that
the bioavailability of ß-carotene was equally poor for all
subjects.

Thus, the main reason for the finding that iron status was not
improved by vegetables seems to be that the iron has poor
bioavailability and the amount provided was small, whereas the
main reason for the finding that vitamin A status was not
improved by vegetables seems to be that it was too difficult to
break down the matrix in which the carotenoids are captured in
the leaves and the complex that they form with proteins for
photosynthesis. The difficulty in freeing ß-carotene from its
matrix might have been aggravated by parasitic infestations.

Conclusion

Because only very few food-intervention studies have looked at
iron status, and because the available results are contradictory,
no firm conclusions can be drawn as to whether or not vegetables
can improve iron status. It is necessary to conduct similar
intervention studies with foods of both plant and animal origin
and with fortified foods, and to investigate ways to improve the
bioavailability of nutrients. Alternative approaches, such as
food fortification and promotion of animal foods rich in haem
iron and retinol, must be considered. In the meantime, the use of
other strategies that have proved to be effective to reduce iron
and vitamin A deficiencies should continue.

Anaemia is associated with increased perinatal mortality,
increased child morbidity and mortality, behavioural changes and
impaired mental development, decreased work performance,
increased susceptibility to lead poisoning, and impaired immune
competence. Iron-deficiency anaemia is an intractable problem, as
indicated by the goal set by world leaders of reducing
nutritional anaemia to one-third of 1990 levels by the year 2000,
compared with the goals of virtually eliminating deficiencies of
vitamin A and of iodine during the same period. To a large
extent, this is because intake is less associated with status for
iron than for iodine and vitamin A. The demand for iron varies
throughout the life cycle, and the bioavailability of iron varies
over a wide range because of a number of factors, such as the
species of iron compound, the molecular linkage, the amount of
nutrient consumed in a meal, the matrix in which the nutrient is
incorporated, the absorption modifiers, the nutrient status of
the host, genetic factors, other host-related factors, and
interactions among factors.

Introduction

Iron deficiency is a problem in both developed and developing
countries, affecting about 1,000 million people worldwide,
including 370 million women of child-bearing age. In developed
countries, it is primarily a problem of these women and young
children, and usually occurs as an isolated nutritional problem.
In developing countries, such as Indonesia, it extends to older
children and usually occurs together with deficiencies of other
nutrients [1].

Because of the magnitude of the problem and its serious
consequences, a series of meetings has been held in recent years,
beginning with the World Summit for Children in New York in 1990,
followed in 1991 by the conference on Ending Hidden Hunger in
Montreal, and culminating in 1992 with the International
Conference on Nutrition in Rome. These led to declarations by
heads of state of most countries of the world committing their
countries to reducing iron-deficiency anaemia in women of
childbearing age to one-third of 1992 levels by the year 2000
[2]. Such a limited goal, compared with the goals of virtually
eliminating deficiencies of vitamin A and of iodine, is an
admission of the intractability of the problem of iron-deficiency
anaemia.

Consequences of iron deficiency

As shown in a series of studies in Indonesia and other
countries, attention, learning achievement, and mental
development are affected by anaemia in children [3, 4], and these
effects can be reversed by iron supplementation when the children
are under the age of 10 years but not older [5]. In addition, in
Indonesia, iron-deficient rubber plantation labourers were less
productive than workers with normal haemoglobin concentrations,
and iron supplementation improved their performance [6]. Work
performance was particularly impaired when the haemoglobin
concentration fell below 100 g/L, which is 20 to 40 g/L below the
lower limit of normal for adults. From the point of view of a
government, impairments of mental development and work
performance are good reasons to combat iron-deficiency anaemia.

From the point of view of the individual, other aspects of
iron deficiency also assume importance. Decreased resistance to
infection is due to impairment of both specific and non-specific
defense mechanisms. Impairment of specific immunity is
particularly noticeable with cell-mediated immunity, whereas
oxygen-dependent killing rather than phagocytosis is the most
important aspect of non-specific immunity that is affected. An
impaired capacity to maintain body temperature in a cold
environment is characteristic of iron-deficiency anaemia [7].
Another consequence is lead poisoning, the risk of which is
increased in anaemic children, particularly when they are young
[8]. Reducing the lead in petrol rather than improving iron
status may be the most effective way of approaching this problem.
Finally, iron-deficiency anaemia during pregnancy has very
serious consequences, leading to increased risk of perinatal
mortality and to increased infant mortality [2].

Measuring prevalence of iron deficiency and of
iron-deficiency anaemia

In a research environment, a battery of haematological and
biochemical measurements can be made, such as haemoglobin,
haematocrit, mean corpuscular volume, serum transferrin, serum
iron (and transferrin saturation), serum ferritin, free
erythrocyte protoporphyrin, and transferrin receptor. However,
these methods are generally inappropriate in an operational
environment where haemoglobin distribution curves can be used
[9]. A shift to the left, compared with a population without
anaemia, is indicative of anaemia. In areas where the anaemia is
due to iron deficiency, such a shift is seen only in children and
women, not in men. If the distribution in men is also shifted to
the left, it indicates anaemia due to infection or infestation
such as from malaria or from hookworm.

Methods of combating iron deficiency

Several possible approaches to combating iron-deficiency
anaemia exist. The most obvious is supplementation with iron
preparations. Until the present time, this has been the principal
method used in developing countries. Programmes often were
ineffective, however, because the target group was not reached,
compliance was poor, and the preparations used sometimes had low
bioavailability of iron [10]. Compliance will almost certainly be
increased when daily schedules are replaced by weekly schedules
[10] and when the preparations used contain iron in a more
bioavailable form.

Food fortification has proved effective in reducing
iron-deficiency anaemia, particularly in the United States. The
reason for this is not only that American industry is able to
manufacture and market iron-fortified products, but also that
legislation and accompanying regulations allow fortification to
be maintained. By contrast, in many countries in Europe,
legislation and regulations are very restrictive with respect to
food fortification.

The technology for fortifying foods with iron has improved
much in recent years. Problems of offflavour have been overcome,
and compounds with higher iron bioavailability, such as ferrous
fumarate, have been introduced. However, increasing
bioavailability by removing inhibitors of iron absorption through
fermentation and use of phytases can be effective and, combined
with enhancing bioavailability through increased consumption of
enhancers such as ascorbic acid, may make fortification
unnecessary. This is an area in which much more applied and
operations research applicable to developing countries has to be
done.

Iron supply can be increased not only by choosing animal
products rich in haem iron but also by choosing traditional
iron-rich plant foods. Recently, much interest has been expressed
in increasing the total amount of iron and the proportion per
content that is bioavailable through breeding and genetic
engineering [11]. It remains to be seen what can be achieved by
these means.

Any programme to control iron deficiency has to take into
account other nutrients, infection, and other factors. Folic acid
and vitamin B12 are required for the synthesis of the haem
molecule in haemoglobin. Supplementation with vitamin A increases
haemoglobin levels in anaemic women with marginal or just
adequate vitamin A levels [12], probably by an effect on the
uptake of iron by the erythropoietic system [13]. Riboflavin
supplementation increases haemoglobin levels in
riboflavin-deficient subjects [14], probably predominantly by an
accelerated rate of epithelial turnover in the small intestine
[15].

It is well known that hookworm and malaria are important
aetiological factors in nutritional anaemia, so greater efforts
must be taken not only to increase iron intake but also to reduce
iron losses from these causes. In addition, it should be noted
that oral contraception reduces menstrual blood loss and
intrauterine contraceptive devices generally increase iron loss.

In addition to choosing an approach or series of approaches to
controlling iron-deficiency anaemia, the public has to be
mobilized [16]. This involves advocacy to those responsible for
making decisions about programmes to control iron deficiency. It
is also essential to educate the public to change food habits to
eat more haem iron-containing foods and to eat non-haeme iron
foods that enhance iron bioavailability. The public must be made
aware of the value of consuming foods that enhance non-haem iron
bioavailability with meals (orange juice), and of not consuming
those that inhibit non-haem iron bioavailability (tea).

Bioavailability

Iron bioavailability has been addressed by research workers
[17] but has not yet received the attention it deserves by those
responsible for programmes controlling iron deficiency. It is the
proportion of iron ingested that becomes available to the body
for metabolie processes, and most work in the area is still
guided by the algorithm for iron bioavailability developed by
Monsen and colleagues in 1978 [18]. In this algorithm, the
absorption of haem iron is assumed to be 15% in men and 23% to
35% in women, depending on iron stores. For non-haem iron,
absorption depends on bioavailability (low, medium, high)
estimated in general terms from the phytate, haem, and ascorbic
acid contents of a meal. Thus, for men the range is 2% to 4%, and
for women it is 3% to 20%, also depending on iron stores as
follows:

However, it seems to be time to consider more factors when
calculating bioavailability. Therefore, we propose an approach
that focuses on the following [19] species of iron compound,
molecular linkage, amount of nutrient consumed in a meal, matrix
in which the nutrient is incorporated, absorption modifiers,
nutrient status of the host, genetic factors, other host-related
factors, and interactions.

Species of iron

Iron is probably absorbed only in the ferrous form, so
elemental iron has to be oxidized and ferric iron reduced to
ferrous iron before absorption. Thus, it is important to know the
proportion of the various atomic species in a food.

Molecular linkage

Haem iron is absorbed to a much greater extent than non-haem
iron. In iron-deficient persons, the absorption of haem iron is
about 35% and the absorption of non-haem iron is about 25%, when
enhancers are abundant (see below). The corresponding figures in
an iron-replete subject are 15% and 2%. Enhancers and inhibitors
exert their effect only on the absorption of non-haem iron,
although the inhibition of absorption of non-haem iron by dietary
calcium is an exception. Ferrous iron in the form of fumarate is
absorbed much better than ferrous sulphate.

An additional problem with elemental iron is the particle
size, as fine particles, such as iron reductum produced by
reducing ferrous iron, are absorbed much better than coarser
particles.

Amount of iron in the diet

Iron absorption is reduced to some extent at increased levels
of iron intake. More important, perhaps, is the effect of high
intake that down-regulates the capacity of the intestinal
epithelium to absorb iron subsequently.

Food matrix

Matrix effects are probably more pronounced for non-haem than
for haem iron. This is based on experience with the low
bioavailability of plant carotenoids [20].

Absorption modifiers

A number of compounds in the diet affect the bioavailability
of iron. Ascorbic acid in the diet enhances the absorption of
non-haem iron, probably by reducing ferric iron to ferrous iron,
the form in which iron is probably absorbed from the intestine.
Dietary ascorbic acid probably also prevents the precipitation in
the intestinal lumen of ferric complexes such as ferric
hydroxide. The effect of ascorbic acid on non-haem iron
absorption is marked and strongly dose related, especially for
the first 50 mg of ascorbic acid in a meal.

A second factor is meat, which stimulates non-haem iron
absorption. This is due in part to the haem in the diet, but is
possibly also a result of other dietary factors such as
individual amino acids. Acidic foods also stimulate iron
absorption, which probably explains the stimulatory effects of
fermented foods such as sauerkraut, which is prepared from
cabbage, and enjera, which is prepared from the cereal teff in
Ethiopia.

Phytate (inositol phosphate) is perhaps the most important
dietary constituent inhibiting non-haem iron absorption, but
fortunately its effect can be counteracted by increasing ascorbic
acid intake. It is interesting to note that inositol with up to
three phosphate groups stimulates iron absorption, whereas
inositol with four to six phosphate groups inhibits absorption.
Another powerful inhibitor of absorption is the group of plant
phenolic compounds such as those from tea and coffee, and their
effect is also reversed by dietary ascorbic acid.

Other minerals can influence the absorption of iron. As
mentioned, calcium inhibits the absorption of not only non-haem
but also haem iron. This inhibition is not reversed by ascorbic
acid. Magnesium acts in the same way as calcium and to the same
extent. However, interference from dietary magnesium is less
because the intake is less than that of calcium. Manganese, but
not zinc, in the diet reduces iron absorption.

Nutrient status of the host

Iron status has a marked effect on absorption of iron,
especially non-haem iron. It is affected not only by intake and
absorption but also by iron utilization and losses. Utilization
varies throughout the life cycle, and losses are increased by
menstruation, haemorrhage, blood donation, the action of
parasites such as hookworm, and malaria.

Genetic constitution of the host

Iron overload is a genetic condition in which people absorb
large amounts of iron that is not subject to negative feedback.
The problem can be overcome by introducing a programme of
screening for iron nutriture abnormalities, with the aim of
detecting individuals with anaemia and those with iron overload.

Other host-related factors

Intestinal parasites such as Giardia lamblia and Ascaris
lumbricoides possibly reduce the absorption of iron. Such a
negative effect on bioavailability is quite separate from that of
hookworm in increasing iron loss from the body.

Interactions among the above

All of these factors should be taken into account when
designing a programme to control iron-deficiency anaemia. When
trying to evaluate the magnitude of the effects of these factors,
not only should the effects be quantified independently of one
another, but the interaction among the factors should also be
measured.

It is hoped that in the future we will be able to evaluate the
impact of all these variables on iron absorption. It will then be
possible to come up with mathematical values to fit our proposed
approach, which could replace the algorithm of Monsen et al. that
has served us well for nearly 20 years [18]. Particular attention
should be paid to absorption modifiers and to parasites.

Conclusion

Iron-deficiency anaemia is a serious problem because of its
impact on individuals and because of the large number of
individuals it affects. Much work has been and is being done to
control the problem, but programmes should pay more attention to
increasing iron bioavailability rather than iron intake.

12. Suharno D, West CE, Muhilal, Karyadi D, Hautvast JGAJ. Not
only supplementation with iron but also with vitamin A is
necessary to combat nutritional anaemia in pregnant women in west
Java, Indonesia. Lancet 1993;342:1325-8.

13. Roodenburg AJC, West CE, Shiguang Yu, Beynen AC.
Comparison between time-dependent changes in iron metabolism of
rats as induced by marginal deficiency of either vitamin A or
iron. Br J Nutr 1994;71:687-99.